JP2013-236201A and JP2014-127754A disclose techniques for responding to an incoming voice call to a cellular phone without a user operating an operating unit. JP2013-236201A discloses a cellular phone that, in the case where it is determined that the phone is in a predetermined orientation, transits from a call receiving state to a voice call state under the condition that a proximity sensor located in the vicinity of a mouthpiece detects that the phone is near an operator's ear and a rear-side proximity sensor does not detect an object such as a table. JP2014-127754A discloses a cellular phone responding to an incoming call and executing voice call processing in the case where it is detected that the phone has approached a user.
JP2014-127754A also discloses a cellular phone placing a response into an on-hold state in the case where the phone detects that a user is not holding the phone after a call is received, and stopping the transmission of inputted voice in the case where the phone detects that the user has moved away after voice call processing has started. JP-S63-304753A discloses a phone placing a voice call in an on-hold state in the case where it is detected that a receiver of the phone has been placed horizontally.